1. Field of the Invention
The present invention relates generally to drive mechanisms for disk-type recording media. In particular, the present invention is a magneto-optic disk drive.
2. Description of the Prior Art
Magneto-optic data recording technology combines the erasability features of magnetic data storage systems with the high data storage capacity of optical systems. A five and one-quarter inch magneto-optic disk can hold up to six hundred M bits of information, which is one thousand or more times the amount of information presently stored by a magnetic floppy diskette of similar size. Magneto-optic disks are also transportable and can be transferred between drives. Since the read, write and erase operations are performed with light beams rather than mechanical heads, they have long life, high reliability, and are relatively immune to physical wear.
The principles of magneto-optic technology are well known. Information is digitally stored at bit positions on a magneto-optic disk. Typical bit positions have a diameter of 0.8 to 2.0 microns. The orientation of the magnetic field at each bit position can be switched between a digital one state in which its north pole is oriented upward, and a digital zero state in which the magnetic field is reversed and the north pole is oriented downward. The orientation of the magnetic field at each bit position is selected by subjecting the bit position to the magnetic field of the appropriate polarity, and heating the bit position of the disk. The magnetic orientation of the bit position is frozen when the disk cools and returns to room temperature.
The magnetic fields of all bit positions in unwritten disks will generally be oriented north poles down to represent a digital zero When writing information, the bit positions will be subjected to a write magnetic bias field and heated by a high intensity laser beam. The orientation of the magnetic fields at the written bit positions will then reverse to north poles up. Bit positions are erased by subjecting them to an erase bias field of the opposite polarity, and again heating the bit. The magnetic field orientation at the erased bit positions will then reverse and switch to north poles down.
Data is read from the optical disk using a low-power laser beam. Because of the magneto-optic phenomena known as the Kerr-effect, the polarization of a laser beam impinged upon the bit positions will be rotated as a function of the magnetic orientation of the bit. The polarization of the laser beam portions reflected from bit positions on the optical disk is detected by optoelectronic detector circuitry. Signals from the detector circuitry are processed to determine whether the bit position is representative of a digital one or a digital zero.
For purposes of convenience and protection, the optical disk is typically positioned within an enclosure to form a cassette. The cassette is loaded into an optical disk drive which is interfaced to a personal computer or other data processing system and includes the mechanical and electrical subsystems required to write, read and erase data on the optical disk. Optical disk drives typically include an optical head having an objective lens for focusing the laser beam onto the optical disk, a drive motor for rotating the optical disk, a focus servo system and a tracking servo system. After the cartridge is inserted into the drive and its door is opened, the disk drive motor and optical head are moved with respect to the optical disk to bring the drive motor and disk into engagement, and the optical head into its operating position adjacent the disk. In one known drive the optical head and drive motor are mounted to a frame pivotally suspended within the drive to form an assembly. After the disk is loaded into the drive, the assembly is driven to an operative position at which the drive motor engages the disk and the optical head is positioned adjacent the disk. The cartridge is loaded into and removed from the drive when the assembly is in a load/unload position spaced from the disk.
The tracking servo system is a closed force-position loop which includes an actuator for driving and positioning the optical head or objective lens about a tracking axis with respect to servo tracks on the optical disk. In one known CD player the optical head is positioned on an elongated arm opposite a pivot mechanism from a counterweight. The arm and optical head are driven about a tracking axis by a pair of electromagnetic motors, one positioned between the pivot mechanism and each of the optical head and counterweight. Another known magnetic disk drive includes a V-shaped arm having two legs. The arm is movably mounted adjacent the disk by a pivot mechanism located at the arm vertex. The magnetic head is mounted at the free end of one arm, while the electromagnetic motor is mounted to the free end of the other. Pivot bearing and arm dynamics, including play in the bearing and bending of the arm, significantly affect the overall performance of these tracking servo systems.
The focus servo system, also a closed force-position loop, includes a focus actuator which drives and positions the objective lens about a focus axis with respect to the optical disk. The focus servo system controls the focus actuator in such a manner as to keep the laser beam properly focused onto the optical disk. Linear electromagnetic motors are typically used as actuators.
Other known optical disk drive mechanisms and associated tracking and focus servo systems are disclosed generally in the following United States patents:
______________________________________ 3,940,148 Torrington et al. 3,983,317 Glorioso 4,135,721 Camerik 4,326,284 Elliott 4,340,955 Elliott 4,517,617 Tsuji et al. 4,519,055 Gilson 4,545,045 Baer et al. 4,545,046 Jansen et al. 4,736,356 Konshak 4,752,922 MacAnally et al. ______________________________________
It is evident that there is a continuing need for improved optical disk drives. Mechanical systems of the drive must be compact and reliable. The effects of physical component dynamics upon tracking servo system response should be mitigated as much as possible to increase the performance of the drive. The drive should also be relatively uncomplicated to facilitate its assembly in an economically feasible manner. A half-height drive having these characteristics would be especially desirable.